Novel diacetylenic and polydiacetylenic compositions

ABSTRACT

This invention provides a novel class of diacetylenic monomers and corresponding polydiacetylenic polymers. 
     Illustrative of the invention is a polymer characterized by the repeating unit: ##STR1## In the form of an optically transparent medium with a noncentrosymmetric alignment of molecules, the polymer exhibits exceptional second order nonlinear optical susceptibility effects.

This is a division of application Ser. No. 854,273 filed Apr. 21,1986.

BACKGROUND OF THE INVENTION

The field of nonlinear optics has potential for important applicationsin optical information processing, telecommunications and integratedoptics.

Recently it has been recognized that organic and polymeric materialswith large delocalized π-electron systems can exhibit nonlinear opticalresponse, which in many cases is a much larger response than byinorganic substrates.

In addition, the properties of organic and polymeric materials can bevaried to optimize other desirable properties, such as mechanical andthermoxidative stability and high laser damage threshold, withpreservation of the electronic interactions responsible for nonlinearoptical effects.

Thin films of organic or polymeric materials with large second-ordernonlinearities in combination with silicon-based electronic circuitryhave potential as systems for laser modulation and deflection,information control in optical circuitry, and the like.

Other novel processes occurring through third-order nonlinearity such asdegenerate four-wave mixing, whereby real-time processing of opticalfields occurs, have potential utility in such diverse fields as opticalcommunications and integrated circuit fabrication.

Of particular importance for conjugated organic systems is the fact thatthe origin of the nonlinear effects is the polarization of theπ-electron cloud as opposed to displacement or rearrangement of nuclearcoordinates found in inorganic materials.

U.S. Pat. No. 4,431,263 describes nonlinear optical materials based onpolymerized diacetylenes. There is a detailed elaboration of physicaland theoretical principles which underlie nonlinear behavior in organicsystems. Reference is made to Physical Review A, 20 (No. 3), 1179 (1979)by Garito et al, entitled "Origin of the Nonlinear Second-Order OpticalSusceptibilities of Organic Systems".

Other United States patents which describe the synthesis and propertiesof diacetylenes and polydiacetylene compositions include U.S. Pat. Nos.2,,855,441; 3,065,283; 3,923,622; 3,994,867; 3,999,946; 4,125,534;4,195,055; 4,195,058; 4,208,501; 4,215,208; 4,242,440; 4,255,535;4,328,259; 4,339,951; 4,389,217; 4,439,346; 4,439,514; and prior artcited therein, incorporated herein by reference. British Pat. No.1,154,191 is of related interest.

Other technical publications which describe diacetylenic propertiesinclude Makromol. Chem., 180, 2975 (1979); 182, 965 (1981); 182, 1363(1981); Mol. Cryst. Liq. Cryst., 93, 239 (1983); 93 247 (1983); 93, 261(1983); and prior art cited therein, incorporated herein by reference.

Nonlinear optical properties of organic and polymeric materials was thesubject of a symposium sponsored by the ACS division of PolymerChemistry at the 18th meeting of the American Chemical Society,September 1982. Papers presented at the meeting are published in ACSSymposium Series 233, American Chemical Society, Washington, D.C., 1983.Chapters 1 and 8-11 review studies relating to nonlinear opticalproperties of polydiacetylenes; incorporated herein by reference.

There is continuing research effort to develop new nonlinear opticalorganic systems for prospective novel phenomena and devices adapted forlaser frequency conversion, information control in optical circuitry,light valves and optical switches. The potential utility of organicmaterials with large second-order and third-order nonlinearities forvery high frequency application contrasts with the bandwidth limitationsof conventional inorganic electrooptic materials.

Accordingly, it is an object of this invention to provide a novelpolymeric composition having an extended conjugated polyunsaturatedstructure.

It is another object of this invention to provide a thermoplasticpolydiacetylenic composition having anisotropic properties.

It is another object of this invention to provide a polydiacetyleniccomposition which exhibits exceptional nonlinear optical effects.

It is another object of this invention to provide a polymeric nonlinearoptical medium which possesses a unique combination of thermoxidativestability and high laser damage threshold.

It is a further object of this invention to provide a novel class ofconjugated diacetylenic monomers.

Other objects and advantages of the present invention shall becomeapparent from the accompanying description and example.

DESCRIPTION OF THE INVENTION

One or more objects of the present invention are accomplished by theprovision of a polymeric composition which is characterized by therecurring monomeric unit: ##STR2## where X is an electron-donatingsubstituent; Y is an electron-withdrawing substituent; and n is aninteger of at least 3.

The term "electron-donating" as employed herein refers to organicsubstituents which contribute π-electrons when the conjugated electronicstructure is polarized by the input of electromagnetic energy.

The term "electron-withdrawing" as employed herein refers toelectronegative organic substituents which attract π-electrons when theconjugated electronic structure is polarized by the input ofelectromagnetic energy.

Illustrative of eIectron-donating substituents as represented by X inthe above formula are amino, alkylamino, dialkylamino, 1-piperidino,1-piperazino, 1-pyrrolidino, acylamino, hydroxyl, thiolo, alkylthio,arylthio, alkoxy, aryloxy, halo, alkyl, and the like.

Illustrative of electron-withdrawing substituents as represented by Y inthe above formula are nitro, cyano, trifluoromethyl, acyl, carboxy,alkanoyloxy, aryloxy, alkoxysulfonyl, aryloxysulfonyl, and the like.

In another embodiment the present invention provides a polyacetyleniccomposition having anisotropic properties which is characterized by therecurring monomeric unit: ##STR3## where R and R¹ are alkyl groupscontaining between about 1-20 carbon atoms, and R and R¹ taken togetherwith the connecting nitrogen atom form an alicyclic substituent; Y' is asubstituent selected from nitro, cyano and trifluoromethyl radicals; andthe weight average molecular weight of the polymer is in the rangebetween ahout 1000-500,000.

Illustrative of alkyl groups are methyl, ethyl, butyl, isobutyl, hexyl,decyl, hexadecyl, eicosyl, and the like.

In another embodiment this invention provides a process for productionof a polydiacetylenic composition which comprises polymerizing adiacetylene monomer corresponding to the formula: ##STR4## where X is anelectron-donating substituent, Y is an electron-withdrawing substituent,and m is the integer one or two.

The polymerization reaction proceeds readily if the acetylene monomer isexposed to ultraviolet radiation, or if the monomer is heated to atemperature sufficiently high for initiation of the polymerizationreaction.

In a typical procedure the acetylene monomer is heated to form ananisotropic melt phase and as necessary the temperature is elevateduntil the polymerization reaction is initiated and completed. Thepolymerization reaction temperature usually will be in the range betweenabout 200°-275° C. A polymerization catalyst such as a peroxide can beemployed if it is desirable to accelerate the rate of polymerization.

A film of the polydiacetylenic composition can be prepared by forming athin substrate of the diacetylene monomer in a highly ordered state, andthen polymerizing the monomer in the substrate to form a correspondingthin polymeric film.

A present invention polydiacetylenic composition can be formed intosheets, films, fihers or other shaped articles by conventionaltechniques such as extrusion, molding or casting.

The weight average molecular weight of a present inventionpolyacetylenic composition can be controlled within the range betweenabout 1000-500,000, depending on the reactivity of the diacetylenemonomer and the polymerization conditions. In terms of inherentviscosity (I.V.), the preferred polydiacetylenes commonly will exhibitan I.V. of about 2.0-10.0 dl/g when dissolved in a concentration of 0.1percent by weight in pentafluorophenol at 60° C.

Diacetylene Monomer Synthesis

In another embodiment this invention provides a novel class ofconjugated diacetylenic monomers corresponding to the formula: ##STR5##where R and R¹ are alkyl groups containing between about 1-20 carbonatoms, and R and R¹ taken together with the connecting nitrogen atomform an alicyclic substituent; and Y' is a substituent selected fromnitro, cyano and trifluoromethyl radicals.

Illustrative of the novel diacetylene compounds are1-(4-dimethylaminophenyl)-4-(4-nitrophenyl)-1,3-butadiyne;1-(4-dimethylaminophenyl)-4-(4-cyanophenyl)-1,3-butadiyne;1-(4-dimethylaminophenyl)-4-(4-trifluoromethyl)-1,3-butadiyne; and thelike.

The diacetylene monomers utilized for the preparation of the presentinvention polydiacetylenic compositions can be synthesized byconventional procedures such as the general methods described inreferences listed in the Background of the Invention disclosurehereinabove.

The following flow diagram illustrates a reaction scheme for synthesisof a diacetylene compound: ##STR6##

Nonlinear Optical Properties

In another embodiment this invention provides a polydiacetyleniccomposition having nonlinear optical properties which is characterizedby the recurring monomeric unit: ##STR7## where said polymer has aweight average molecular weight in the range between about 2000-100,000.

In another embodiment this invention provides a polydiacetyleniccomposition having nonlinear optical properties which is characterizedby the recurring monomeric unit: ##STR8## where said polymer has aweight average molecular weight in the range between about 2000-100,000.

In another embodiment this invention provides a polydiacetyleniccomposition having nonlinear optical properties which is characterizedby the recurring monomeric unit: ##STR9## where said polymer has aweight average molecular weight in the range between about2000-1000,000.

The polydiacetylenic compositins illustrated above exhibit aTHG.sub.χ.sup.(3) susceptibility value greater than about 10×10⁻¹² esu.The THG .sub.χ.sup.(3) response time is less than that about 1×10⁻¹⁴second.

The fundamental concepts of nonlinear optics and their relationship tochemical structures can be expressed in terms of dipolar approximationwith respect to the polarization induced in an atom or molecule by anexternal field.

As summarized by Twieg and Jain in chapter 3 of ACS Symposium Series233, the fundamental equation (1) below describes the change in dipolemoment between the ground state μ_(g) and an excited state μ_(e)expressed as a power series of the electric field E which occurs uponinteraction of such a field, as in the electric component ofelectromagnetic radiation, with a single molecule. The coefficient α isthe familiar linear polarizability, β and γ are the quadratic and cubichyperpolarizabilities, respectively. The coefficients for thesehyperpolarizabilities are tensor quantities and therefore highlysymmetry dependent. Odd order coefficients are nonvanishing for allmolecules, but the even order coefficients such as β (responsible forsecond harmonic generation, SHG) are zero for centrosymmetric molecules.The odd order coefficient γ is responsible for third harmonic generation(THG).

Equation (2) is identical with (1) except that it describes amacroscopic polarization, such as that arising from an array ofmolecules in a crystal.

    Δμ=μ.sub.e -μ.sub.g =αE+βEE+γEEE+. . . (1)

    P=P.sub.0 +χ.sup.(1) E+χ.sup.(2) EE+χ.sup.(3) EEE+. . . (2)

Light waves passing through an array of molecules can interact with themto produce new waves. This interaction may be interpreted as resultingfrom a modulation in refractive index or alternatively as a nonlinearityof the polarization. Such interaction occurs most efficiently whencertain phase matching conditions are met, requiring identicalpropagation speeds of the fundamental wave and harmonic wave.Birefringent crystals often possess propagation directions in which therefractive index for the fundamental ω and the second harmonic 2ω areidentical so that dispersion may be overcome.

A present invention polydiacetylenic medium typically is an opticallyclear thin film which exhibits hyperpolarization tensor properties suchas second harmonic and third harmonic generation, and the linearelectrooptic (Pockels) effect. For second harmonic generation, the bulkphase of the polymeric substrate does not possess a real ororientational average inversion center; the substrate is anoncentrosymmetric dipolar structure.

In another embodiment this invention provides a nonlinear optical mediumcomprising a noncentrosymmetric configuration of aligned molecules of apolymer characterized by the recurring monomeric unit: ##STR10## where Xis an electron-donating substituent; Y is an electron-withdrawingsubstituent; and n is an integer of at least 3; and wherein thenonlinear optical medium exhibits a Miller's delta of at least onesquare meter/coulomb.

For purposes of the present invention, a diacetylenic monomer or polymeris adapted to exhibit the external field-induced macroscopicnonlinearity required for second order harmonic generation.

In another embodiment this invention provides nonlinear opticallytransparent host polymeric substrates having incorporated therein adistribution of guest diacetylenic monomer, oligomer or polymermolecules.

Illustrative of this type of optical substrate is a polymethylmethacrylate film containing a distribution of polydiacetylenicmolecules.

If the distribution of guest molecules is random, there is orientationalaveraging by statistical alignment of the dipolar molecules in thepolymeric host, and the optical substrate exhibits third ordernonlinearity (χ.sup.(3)).

If the distribution of guest molecules is at least partially uniaxial inmolecular orientation, then the optical substrate exhibits second ordernonlinearity (χ.sup.(2)). One method for preparing polymeric films withlarge second-order nonlinear coefficients is to remove the orientationalaveraging of a dopant molecule with large β by application of anexternal DC electric field to a softened film. This can be accomplishedby heating the film ahove the host polymer glass-transition temperatureT_(g), then cooling the film below T_(g) in the presence of the externalfield. The poling provides the alignment predicted by the Boltzmanndistribution law.

The formation of a thin host polymer substrate containing guestmolecules having, for example, uniaxial orthogonal molecular orientationcan be achieved by inducing a dipolar alignment of the guest moleculesin the substrate with an externally applied field of the type describedabove.

In one method a thin film of the host polymer (e.g., polymethylmethacrylate) containing guest molecules (e.g., polydiacetylenicpolymer) is cast between electrode plates. The host polymer substratethen is heated to a temperature above the second order transitiontemperature of the host polymer. A dc electric field is applied (e.g.,at a field strength between about 400-100,000 V/cm) for a periodsufficient to align the guest molecules in a unidirectionalconfiguration parallel to the transverse field. Typically theorientation period will be in the range between about one second and onehour, as determined by factors as guest molecular weight and fieldstrength.

When the orientation of guest molecules is complete, the host polymersubstrate is cooled below its second order transition temperature, whiethe substrate is still under the influence of the applied dc electricfield. In this manner the uniaxial molecular orientation of guestmolecules is immobilized in a rigid structure.

The uniaxial molecular orientation of the guest molecules in the hostpolymer substrate can be confirmed by X-ray diffraction analysis.Another method of molecular orientation measurement is by opticalcharacterization, such as optical absorption measurements by means of aspectrophotometer with a linear polarization fixture.

Harmonic generation measurements relative to quartz can be performed toestablish the value of second order and third order nonlinearsusceptibility of the optically clear substrates.

A suitable apparatus for harmonic generation is schematicallyrepresented in Macromolecules, 15, 1386 (1982). The apparatus is aQ-switched Nd³⁺ /YAG laser configured as an unstable resonator withpolarization output coupling. The laser is operated just abovethreshold, supplying 2-5 per pulse of 1.06 μm radiation, which isfocused on the surface of the thin substrate (20-30 μm thickness).Variation of the laser polarization is accomplished with adouble-quarter wave rhomb rotator. The harmonic light is collected withf/16 optics, filtered from the fundamental light, and passed through a20-cm focal length grating monochromator with an 8-nm bandwidth.Detection is accomplished with an 11-stage amplified photomultipliertube. The system is integrated with a computer-controlled gatedelectronic detection and digitization apparatus. The term "thinsubstrate" as employed herein refers to a continuous phase solid film,sheet or coating which has a thickness between about 10-500 microns. Theterm "optically clear" as employed herein refers to a medium which istransparent or light transmitting with respect to incident fundamentallight frequencies and harmonic light frequencies. In an electroopticlight modulator device, a present invention nonlinear optical lensmedium is transparent to both the incident and exit light frequencies.The term "Miller's delta" as employed herein with respect to secondharmonic generation (SHG) is defined by Garito et al in Chapter 1,"Molecular Optics:Nonlinear Optical Properties Of Organic And PolymericCrystals"; ACS Symposium Series 233 (1983)

The quantity "delta" (δ) is defined by the equation:

    D.sub.ijk =ε.sub.o χ.sub.ii χ.sub.jj χ.sub.kk δ.sub.ijk

where terms such as χ_(i).sup.(1) are the linear susceptibilitycomponents, and d_(ijk), the second harmonic coefficient, is definedthrough

    χ.sub.ijk (-2ω; ω, ω)=2d.sub.ijk (-2ω; ω, ω)

The Miller's delta (10⁻² m² /c at 1.06 μm) of various nonlinear opticalcrystalline substrates are illustrated by KDP (3.5), LiNbO₃ (7.5), GaAs(1.8) and 2-methyl-4-nitroaniline (160).

In another embodiment this invention provides an electrooptic lightmodulator device with a polymeric nonlinear optical component comprisingan optically transparent medium of a polymer characterized by therecurring monomeric unit: ##STR11## where X is an electron-donatingsubstituent; Y is an electron-withdrawing substituent; and n is aninteger of at least 3.

In a further embodiment this invention provides an electrooptic lightmodulator device with a polymeric nonlinear optical component comprisingan optically transparent medium of a polymer characterized by therecurring monomeric unit: ##STR12## where R and R¹ are alkyl groupscontaining between about 1-4 carbon atoms, and R and R¹ when takentogether with the connecting nitrogen atom from an alicyclicsubstituent; Y' is a substituent selected from nitro, cyano andtrifluoromethyl radicals; and the weight average molecular weight of thepolymer is in the range between about 1000-500,000.

Physical Properties

A present invention polydiacetylenic substrate exhibits a uniquecombination of properties which are adapted for high strength-low weightapplications.

A present invention sheet, film or fiber is characterized by a hightensile modulus. It also has excellent thermoxidative stability, and ahigh laser damage threshold.

The excellent physical properties are attributable mainly to thechemical structure of the polymer molecule chain which consists of anextended resonance-stabilized conjugated unsaturated configuration, andwhich does not contain any hydrogen atoms in the polymeric backbone.

The following Examples are further illustrative of the presentinvention. The specific ingredients and processing parameters arepresented as being typical, and various modifications can be derived inview of the foregoing disclosure within the scope of the invention.

EXAMPLE

This Example illustrates the preparation and polymerization of1-(4-dimethylaminophenyl)-4-(4-nitrophenyl)-1,3-butadiyne.

A. Synthesis Of 4-Nitrophenyltrimethylsilylacetylene ##STR13##

A one liter three-necked flask equipped with a mechanical stirrer, acondenser, and argon inlet and outlet is charged with 33 g (0.163 mole)of 1-bromo-4-nitrobenzene, 0.9g ofdichlorobis(triphenylphosphine)palladium, 180 ml of anhydrous pyridine,12.0 ml of triethylamine and 25 g (0.255 mole) oftrimethylsilylacetylene.

The admixture is reacted at 72° C. for 6 hours, and then the resultingreaction product mixture is poured into an ice-cold solution of 600 mlof hydrochloric acid in 1500 ml of water to precipitate the product fromsolution. The solid product is recovered by filtration to provide aquantitative yield of 4-nitrophenyltrimethylsilylacetylene, m.p.95°-100° C. Infrared spectral analysis indicates an absorption peak at2170 cm⁻¹ for the acetylene function.

If 1-bromo-4-cyanobenzene or 1-bromo-4-trifluoromethylbenzene isemployed in place of 1-bromo-4-nitrobenzene, then the corresponding4-cyano or 4-trifluoromethyl substituted product is obtained.

B. Synthesis Of 4-Nitrophenylacetylene ##STR14##

4-Nitrophenyltrimethylsilylacetylene is reacted at ambient temperaturefor 3 hours with 3 g of potassium carbonate in 300 ml of methanol. Theresulting reaction product mixture is poured into 1500 ml of distilledwater to precipitate crude 4-nitrophenylacetylene product. The crudeproduct is separated by filtration, washed with water, and dried in avacuum oven at 50° C. and 1 Torr.

Recrystallization from 3 liters of hexane produces 18.8 g (87.9% overallyield based on 1-bromo-4-nitrobenzene) of pure 4-nitrophenylacetylene,m.p. 150° C. Infrared spectral analysis indicates absorption peaks at2100 (C.tbd.C) and 3270 (.tbd.CH) cm⁻¹.

C. Synthesis Of 1-Bromo-2-(4-nitrophenyl)acetylene ##STR15##

A solution of 5.88 g of 4-nitrophenylacetylene in 50 ml oftetrahydrofuran is added to 10 ml of sodium hypobromite solution, andthe admixture solution is stirred at ambient temperature for 16 hours.

A solution of 5 g of ammonium chloride in 15 ml of water is added to thereaction medium to destroy the excess sodium hypobromite. The resultingreaction product mixture is poured into 1500 ml of water to precipitatea crude product. The crude product is separated by filtration, washedwith water, to yield 9.1 g of 1-bromo-2-(4-nitrophenyl)acetylene, m.p.170° C. Infrared spectral analysis indicates an absorption at 2200 cm⁻¹for acetylene (C.tbd.C).

D. Synthesis Of1-(4-N,N-dimethylaminophenyl)-4-(4-nitrophenyl)-1,3-butadiyne. ##STR16##

A 300 ml three-necked flask equipped with a mechanical stirrer, anaddition funnel, and nitrogen inlet and outlet is charged with 0.747 gof hydroxylamine hydrochloride, 15 ml of butylamine, 15 mg of cuprouschloride and 1.59 g of 4-N,N-dimethylaminophenylacetylene.

A solution of 3.07 g (0.0136 mole) of 1-bromo-4-nitrophenylacetylene in50 ml of tetrahydrofuran is added dropwise to the admixture in thereactor over a period of 30 minutes at a temperature of 20° C. Thereaction mixture is maintained at 38° C. for 1.5 hours, and then pouredinto ice water to precipitate a crude product. The crude product isseparated by filtration, washed with water, and chromatographed onsilica gel to yield purified1-(4-N,N-dimethylaminophenyl)-4-(4-nitrophenyl)-1,3-butadiyne.

If 4-(1-piperazyl)phenylacetylene or 4-butoxyphenylacetylene is employedin place of 4-N,N-dimethylaminophenylacetylene, then the corresponding4-(1-piperazyl) or 4-butoxy product is obtained.

E. Preparation Of Polymer ##STR17##

A sample of 1-(4-N,N-dimethylaminophenyl-4-(4-nitrophenyl)-1,3-butadiynein tetrahydrofuran is cast on an optical glass substrate, and thesolvent is evaporated to form a coating on the substrate.

The coated glass substrate is heated at 250° C. for ten minutes toproduce a transparent continuous film of polymer on the glass surface.

The transparent polymeric film exhibits a third order nonlinear opticalsusceptibility χ.sup.(3) value of about 6×10⁻¹² csu as determined by themethod described on page 7 by Garito in "Nonlinear Optical Properties ofOrganic and Polymeric Materials", ACS Symposium Series 233, AmericanChemical Society, Washington, D.C. 1983.

If the polymer film is heated above its glass transition temperaturewhile under the influence of a DC electric field, and then cooled belowthe glass transition temperature while still under the influence of theapplied DC electric field (e.g., a field strength between about1000-50,000 V/cm), a noncentrosymmetric molecular orientation of polymermolecules is achieved.

The film with an external field-induced noncentrosymmetric macroscopicorientation of polymer molecules exhibits second order nonlinear opticalsusceptibility χ.sup.(2) properties.

A present invention transparent polymeric medium is applicable as anonlinear optical component in an electrooptic light modulator device.

What is claimed is:
 1. A diacetylene compound corresponding to the formula: ##STR18## where R and R¹ are alkyl groups containing between about 1-20 carbon atoms, and R and R¹ taken together with the connecting nitrogen atom form an alicyclic substituent; and Y' is a substituent selected from nitro, cyano and trifluoromethyl radicals.
 2. 1-(4-Dimethylaminophenyl)-4-(4-nitrophenyl)-1,3-butadiyne.
 3. 1-(4-Dimethylaminophenyl)-4-(4-cyanophenyl)-1,3-butadiyne.
 4. 1-(4-Dimethylaminophenyl)-4-(4-trifluoromethyl-phenyl)-1,3-butadiyne. 